Distribution of Free Marine Viruses of Lower Chesapeake Bay and Their Effects on Life-History Parameters of the Estuarine Copepod \u3ci\u3eAcartia tonsa\u3c/i\u3e Dana

Abstract

Naturally occurring viruses are very abundant in fresh, estuarine, and marine waters, with densities on the order of 105-108 viruses ml-1. Research has focused on virus effects on bacteria, cyanobacteria, and phytoplankton, as well as mechanisms of virus production and decay. However, little is known about the distribution of viruses in benthic environments or virus effects on organisms in higher trophic levels. To determine the distribution of virus-like particles (VLPs) and bacteria in the lower Chesapeake Bay, vertical profiles of VLPs and bacteria were determined through the water column and 15-25 cm into the sediment at five stations. VLPs were about ten times more abundant in sediment pore water (3.7 x 108 VLPs ml-1) than in the water column (2.4 x 106 bacteria ml-1). In the water column, VLP and bacteria counts exhibited significant differences among stations, with highest values on the southern side of the Bay mouth. In the sediment pore water, VLP abundance varied with depth and was negatively correlated with grain size. Bacteria abundance was highest at the sediment-water-interface, decreased in the first cm of sediment, was uniform in the deeper horizons, and showed no significant relationship with grain size. These are the first data indicating the abundance of VLPs below the surface layer of sediment in aquatic systems and demonstrate that VLPs are components of the sediment microbial community. To evaluate virus effects on zooplankton, concentrated VLPs were added to cultures of Acartia tonsa, then egg production, egg hatching success, and mortality of copepods were measured. Elevated VLP concentrations were obtained by concentrating the virus-size fraction of fresh seawater or water from copepod cultures. Across six experiments, no detrimental effects of viruses on copepods were demonstrated. Similarly, adding pulverized copepods and copepod exudates to water containing healthy copepods yielded no measurable detrimental effect. Therefore, there was no support for the hypothesis that viruses infect and negatively affect the longevity and fecundity of A. tonsa